Have you ever wondered if the whole world around you was a dream, a creation of your own mind? I'll bet you never took it seriously, but the thought must have crossed your mind at some point. The position that the world is a product of your mind (including all the people, animals, rocks, EVERYTHING) is called solipsism. I'm sure you don't believe in solipsism. Solipsism just doesn't feel plausible enough to be believed. Nor is it even plausible enough to be contemplated for more than a brief moment before it is forgotten and abandoned, like a daydream, as you are pulled out of the world of philosophical fantasy and back into the reality of daily routine.
Now for the $64,000 question: how do you know that solipsism is false? You don't believe it, but what rational reason could you spell out for that disbelief? Recently a post was made on a discussion board which I believe conclusively refutes solipsism. In order to understand it is necessary to explain a few things to lay the groundwork for the solution.
Daniel Dennett is a philosopher who has coined the terms 'skyhook' and 'crane' to describe two different types of explanation (See Darwin's Dangerous Idea). A 'skyhook' explanation explains a complex object as the product of something even more complex. Example: my computer (a very complicated object) was designed and built by other human beings (who are, of course, very complicated). A 'crane' explanation takes a complex object and explains it as the result of simpler objects which over time became more complex. Example: Evolution by natural selection.
'Skyhooks' can't serve as ultimate explanations. If you explain item A as the product of a more complex thing (call it item B) which you say the product of an even more complex thing (item C) which was brought into existence by super-complex item D, etc. etc., then your chain of explanation is self-refuting. You can't say that, on the one hand, every complex thing must have an explanation and then turn around and postulate an extremely complex "uncaused first-cause."
Self-contradiction, as it turns out, may be the least of your worries if you want to buy into the "complexity only comes from complexity" theory. You see, postulating an extremely complicated, "uncaused first-cause" can be shown to be improbable on other grounds. Example: suppose that I theorize that the universe was created by a giant super-computer that existed for no reason at all. Such a computer! Can you imagine how many parts it would have, and how precisely they would have to be arranged? After all, you can't just toss together any old combination of metals and plastic and expect to get a working computer. It takes an extremely precise arrangement of matter to create a working computer of even the simplest variety, and if you looked at the number of ways that you could arrange the same molecules that make up the computer, you would find that the vast majority of these arrangements are non-functional. Back to the thought experiment: If I were to postulate a supercomputer that generated the universe, that ought to strike as an astoundingly, jaw-dropping, shit-a-brick ludicrous explanation because it is unlikely that, if some matter and energy existed without a cause or explanation, it would be arranged in such a precise and specific pattern rather than some other, more random and useless, configuration.
To postulate that one's mind is all that truly exists, that one's mind is uncreated, is ludicrous for similar reasons. Perhaps the mind is not a material thing, but whether it is or it isn't, we can be sure of one thing: minds are extremely complicated. Think about the complexity of being able to process, piece together, even create-- information. Such tasks require a very complex and highly precise mind. Now, since we've established that extremely complex and highly specific things are wildly unlikely to be the "uncaused first cause", and since we've established that minds are complex and highly specific, then it follows that the uncaused first cause (if there be one) is very probably not a mind. Since solipsism postulates that your mind (or in my cause, my mind) is a sort of "uncaused first cause" -- the creator of the universe, basically, then it follows that solipsism is very, very, very probably false. Solipsism is a logical possibility, but it is so wildly unlikely, for reasons discussed above, that it need not be given a thought (other than an occasional fun philosophical musing).